1. Field of the Invention
The invention relates to a method for stabilizing a power supply network against fluctuations of the reactive power of an electrical system as claimed in the preamble of patent claim 1, and to a control device of an electrical system as claimed in the preamble of patent claim 6. The electrical system is, in particular, an arc furnace.
2. Discussion of Background
A general problem in power electronics is the product of a wattless component, which produces a reaction on the public power network and interferes with other subscribers to the same network. This is particularly the case when the reactive power varies with time, so that network voltage fluctuations occur which can be seen, for example, as so-called flicker (light fluctuations on luminaries). Such voltage fluctuations occur, for example, in arc furnaces as a result of irregular and uncontrolled changes in the arc.
Widely differing devices are therefore known for stabilizing a power supply network, which attempt to stabilize fluctuations in the reactive load. One conventional method is to vary the triggering angle as a function of the changing load, in order in this way to compensate for the reactive power.
U.S. Pat. No. 5,463,653 describes, for example, such a static VAR compensator (SVC), in which each secondary coil is connected to a thyristor and a freewheeling control loop. The thyristor is triggered with a variable triggering angle in order to obtain a reactive power that is as constant as possible, independently of the changing impedance of the load.
In contrast, U.S. Pat. No. 5,155,740 discloses a flicker compensation device for DC arc furnaces, in which the reactive power is intended to be controlled as a function of a detected reactive power of the arc furnace.
Such compensation devices are complex, and thus relatively expensive.